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Inside Dentistry

December 2012, Volume 8, Issue 12
Published by AEGIS Communications


A “Smart Ceramics” System for Expanded Indications

All-ceramic restorations combine esthetics with conservative preparation.

By David A. Little, DDS

There was a time when porcelain-fused-to-metal (PFM) was the only option for achiev­ing strong and reliable single- and multiple-unit restorations. Metal substructures could make creating lifelike restorations tedious and difficult, as the esthetics were sometimes unpredictable. The advent of superior and innovative technology has made the process of restoring teeth to their original and natural form easy and predictable.1

Since the early 1980s, the range of indications for all-ceramic restorations has been continuously expanded. Driving the trend of rapid development and acceptance of all-ceramic restorations has been the introduction of new ceramic materials with enhanced fatigue strength, as well as innovative cementation procedures. In particular, CAD/CAM technology has brought zirconia (eg, Cercon®, DENTSPLY International, www.dentsply.com; BruxZir®, Glidewell Laboratories, www.glidewelldental.com; and Lava™, 3M ESPE, www.3MESPE.com) to the forefront of restorative dentistry and opened up new indications for all ceramic materials.2 Modern ceramics, such as zirconia, can be employed in the anterior and posterior of the mouth, preserving needed strength and intensifying esthetics.1

Among the zirconia options available is a smart ceramics system (Cercon) that was introduced 12 years ago as a CAM system for fabricating zirconia-based crown-and-bridge frameworks in the dental laboratory. Today, Cercon all-ceramics are appropriate for expanded indications, including custom all-ceramic abutments and implant-supported Cercon frameworks, which can be used to restore both anterior and posterior metal and all-ceramic abutments, as well as natural-tooth preparations.2-6

Cercon ht Zirconia Restorations

Cercon® ht, the new generation of Cercon zirconia, provides outstanding strength and esthetics, and is ideal for full-contour posterior restorations. A notable feature of Cercon ht zirconia restorations is the ultra-thin monolithic material, which contributes maximum strength capabilities. The restorations are milled from a monolithic block of solid yttria-stabilized zirconia. The combination of high flexural strength, high fracture toughness, and partially stabilized zirconia increases the lifespan of restorations.2 Furthermore, chipping—a common problem with layered zirconia restorations—has been eliminated due to scientific technology contributing to the strength and longevity of the material. The level of durability for Cercon ht zirconia—as compared to similar materials after adjusting and repolishing—also demonstrates the material’s safety for opposing antagonist teeth.7,8

The esthetic, metal-free restorations are 26% more translucent at their core than conventional zirconia. This results in the restoration’s blending seamlessly with the patient’s natural dentition for a lifelike, vital appearance.

Other advantages of Cercon zirconia are its simple clinical protocol for conservative tooth reductions, requiring the removal of as little as 0.5 mm to 1 mm of the patient’s natural tooth structure. Additionally, the effortless chairside preparation saves valuable time. Moreover, conventional or adhesive techniques can be used for seating restorations that will fulfill case-specific requirements.2 These features and the corresponding research make Cercon ht zirconia worthwhile for use in numerous cases.

Case Presentation

A 70-year-old man presented with a failing PFM bridge spanning teeth Nos. 3 through 9 (Figure 1 and Figure 2). The abutments were teeth Nos. 3, 6, and 9, with the pontics at the Nos. 4, 5, and 7 positions. Single-unit restorations for teeth Nos. 9 through 12 required repair.

Following a thorough clinical examination, the treatment plan that was discussed with the patient and agreed upon involved a full-contoured zirconia bridge restoration for the posterior and layered zirconia for the anterior restorations (Cercon ht).

Impressions were taken along with a bite registration, facebow, and photographs. This was forwarded to the laboratory (Fort Washington Dental Laboratory, Fort Washington, Pennsylvania) for fabricating indirect provisional restorations (Radica®, DENTSPLY).

The laboratory fabricated the indirect provisional restorations according to the information provided (Figure 3). Indirect provisionals were ideal in this case, because the failing PFM restorations would be replaced with the patient’s natural tooth structure as abutments. Indirect provisionals enabled evaluation of the abutment teeth to ensure that natural, sound tooth structure remained. These provisionals also enabled the dentist and ceramist to incorporate any necessary occlusal adjustments before fabricating the final restorations. And, because the material is esthetic, it served as a “trial smile” for evaluating esthetics. Finally, if any of the patient’s natural dentition required extraction, the provisional could have been easily modified to function following implant placement. In this particular case, the teeth were sound, so extraction was avoided.

The patient’s existing restorations were removed, and the teeth were cleaned and dried. The preparations were then refined to accommodate the anticipated Cercon ht restorations, ensuring chamfers or internally rounded shoulders, 6° to 10° preparation angles, rounded line and point angles, and flattened cusp/fossa plane. The incisal reduction for the anterior restorations was refined to 2 mm to ensure exact reproduction of the internal framework surfaces by the milling unit. For the bridge restoration, the reduction was only 1.5 mm and the taper of the preparation was particularly crucial to ensure that the geometries of all die preparations would facilitate successful CAD/CAM scanning. Parallel or steep preparation walls were avoided to prevent inadequacies during data acquisition and, potentially, insufficient fit. Optimum scannability required a taper of the corresponding walls of the bridge abutments of at least 6°.2

Before placing the provisional restorations, the preparations were cleaned and dried. During the impression-taking technique, the gingival tissues were managed by troughing with a soft-tissue laser to achieve a reproducible and safe representation of the preparation margin. Then, conventional impressions and bite registration were taken using a polysiloxane material (Aquasil Ultra, DENTSPLY).

The provisional restorations were lined with a Bis-GMA provisional material (Integrity® Multi-Cure, DENTSPLY) then trimmed, polished, and cemented in the patient’s mouth (Figure 4). Impressions of the approved provisionals also were taken and sent to the laboratory for use as a matrix for the final crown-and-bridge work.

The laboratory fabricated the posterior full-contoured zirconia restoration and anterior porcelain (Ceramco® PFZ, DENTSPLY) layered zirconia restorations (Figure 5 and Figure 6). At the seating appointment, the provisionals were removed, and the preparations were cleaned and dried. The internal aspects of the restorations were conditioned by micro-roughening and sandblasting with 50-μm aluminum oxide at a maximum pressure of 2 bars. This conditioning improved retention and optimized the bond without adversely affecting the mechanical properties of the restorations.2

A self-adhesive cement (SmartCem®, DENTSPLY) was applied in a thin, uniform layer to the entire internal surfaces of the Cercon ht restorations, then immediately seated in the mouth. Complete seating was verified by gently rocking the restorations to ensure optimal fit.

The self-adhesive cement was allowed to set to a gel consistency, which took approximately 1 minute after complete seating was ensured. Excess cement was then easily removed with a curette and interproximally with floss. Because the zirconia restorations were not light transmittable, the final set was achieved by allowing the cement to self-cure for approximately 6 minutes. Occlusion and esthetics were verified, and the patient was pleased with the definitive results (Figure 7 and Figure 8).6

Conclusion

There are many benefits to using Cercon ht zirconia when fabricating single- or multiple-unit restorations. These benefits include an easy-to-use process, high strength, durability, natural characteristics, true-to-life esthetics, and minimally invasive tooth preparation requirements. Additionally, the ability to seat the restorations using conventional or adhesive techniques is advantageous for satisfying case-specific requirements.

Acknowledgment

The author would like to thank Robert Winkleman CDT, MDT, Fort Washington Dental Lab, for working this case as a team and providing the patient with excellent results.

References

1. Little DA, Crocker JJ. Clinical Use of a New Metal Free Restorative Technology. Case Reports. DENTSPLY Asia Update. 2003;1-3.

2. DENTSPLY International Inc. Cercon ht Full Contour Zirconia. York, Pennsylvania: DENTSPLY International Inc; 2011:1-2.

3. Christensen RP, Ploeger BJ. A clinical comparison of zirconia, metal and alumina fixed-prosthesis frameworks veneered with layered or pressed ceramic: a three-year report. J Am Dent Assoc. 2010;141
(11):1317-1329.

4. Sailer I, Gottnerb J, Kanelb S, Hammerle CH. Randomized controlled clinical trial of zirconia-ceramic and metal-ceramic posterior fixed dental prostheses: a 3-year follow-up. Int J Prosthodont. 2009;22(6):553-560.

5. Al-Amleh B, Lyons K, Swain M. Clinical trials in zirconia: a systematic review. J Oral Rehabil. 2010;37(8):641-652.

6. Schmitt J, Wichmann M, Holst S, Reich S. Restoring severely compromised anterior teeth with zirconia crowns and feather-edged margin preparations: a 3-year follow-up of a prospective clinical trial. Int J Prosthodont. 2010;23(2):107-109.

7. DeguDent A DENTSPLY Company. Cercon® Smart Ceramics Clinical Manual. Germany: DeguDent A DENTSPLY Company; 2009:1-28.

8. Preis V, Behr M, Handel G, et al. Wear performance of dental ceramics after grinding and polishing treatments. J Mech Behav Biomed Mater. 2012;10:13-22.

To read the Laboratory Perspective of this case written by Mr. Winkleman, see the December 2012 issue of Inside Dental Technology, p. 68. dentalaegis.com/go/id458

About the Author

David A. Little, DDS
Private Practice
San Antonio, TX


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Image Gallery

Figure 1 Preoperative close-up retracted view showing the patient’s existing and failing PFM bridge and single-unit restorations.

Figure 1

Figure 2 Preoperative occlusal view of the patient’s defective PFM restorations.

Figure 2

Figure 3 The Radica indirect provisional on the model in the laboratory.

Figure 3

Figure 4 Close-up view of the Radica provisional restorations with the patient in natural smile.

Figure 4

Figure 5 The full-contour Cercon ht zirconia bridge restoration after milling and glazing.

Figure 5

Figure 6 The completed Cercon ht restorations before delivery to the dentist.

Figure 6

Figure 7 Postoperative occlusal view of the definitive Cercon ht zirconia restorations.

Figure 7

Figure 8 Postoperative view of the definitive Cercon ht zirconia restorations with the patient in natural smile.

Figure 8